I would have some suggestions for potential improvements to design usability; however I seem to remember a fundamental issue from last time we tried using this type of method being inconsistency of reading depending on ambient lighting?

I would also suggest a slightly less linear scale (perhaps log, or another) - or at least to try one in comparison to linear; or alternatively perhaps just linear expansion of the 0-5 region, as I suspect that dependent on the environmental light level, most of the judgement will be around the 1-3 region per current printing, with 5-10 being almost constant perceptually.

Also suggest printing the numbers underneath the scale, ideally in the same % vs white; currently some numbers seem lighter which might be confusing/unreadable.